Effect Of Sidelobes Research Articles

Sidelobe Suppression for Likelihood Ratio-Based Seismic Deconvolution

In this work, we develop a novel abrupt-jump detection algorithm for seismic signal deconvolution. This new method significantly suppresses the effect of sidelobes. It begins with transforming a seismic trace to a series of innovations with a Kalman filter and then estimates the likelihood ratios of the reflectivity impulses from the innovations. Second, it modifies the likelihood ratios by imposing additional punishment on its asymmetry. Therefore, the likelihood ratios induced by the sidelobes are highly suppressed. Hence the reflectivity impulses recovered from the modified likelihood ratios are less affected by the sidelobes, leading to significantly enhanced resolution. The efficacy of the proposed method is numerically validated on a synthetic and a field dataset. The experimental results show that the proposed scheme is efficient and practical in enhancing the signal quality of seismograms than the original likelihood-ratio-based abrupt-jump detection.

Influence of Antenna Pattern on Synthetic Aperture Radar Image Sidelobe Level in NDE Applications

The influence of the antenna gain pattern on synthetic aperture radar (SAR) image sidelobe level is analyzed in this article. The traditionally used antenna with wide beamwidth results in relatively constant and large sidelobe level in SAR image. The presence of these sidelobes can mask adjacent weak indications, which often necessitate windowing or implementation of other signal processing techniques in order to help reduce the effect of image sidelobes associated with strong target indications. Alternatively, using an antenna with a relatively narrow beamwidth provides for an inherent weighting function applied to the target spectrum, which is calculated within the SAR algorithm, along the cross-range direction, and this weighting function is directly related to the scanning antenna gain pattern properties. Consequently, an antenna with a relatively narrow beamwidth produces a lower SAR image sidelobe level along the cross-range direction. Corroborating results from numerical simulations and measurements are provided to illustrate the impact of antenna gain pattern on SAR image sidelobe level.

Pre-selection of the candidate fields for deep imaging of the epoch of reionization with SKA1-low

ABSTRACT The Square Kilometre Array (SKA) will be the first low-frequency instrument with the capability to directly image the structures of the epoch of reionization (EoR). Indeed, deep imaging of the EoR over five targeted fields of 20 sq deg each has been selected as the highest priority science objective for SKA1. Aiming at preparing for this highly challenging observation, we perform an extensive pre-selection of the ‘quietest’ and ‘cleanest’ candidate fields in the southern sky to be suited for deep imaging of the EoR using existing catalogues and observations over a broad frequency range. The candidate fields should meet a number of strict criteria to avoid contaminations from foreground structures and sources. The candidate fields should also exhibit both the lowest average surface brightness and smallest variance to ensure uniformity and high-quality deep imaging over the fields. Our selection eventually yields a sample of 7 ‘ideal’ fields of 20 sq deg in the southern sky that could be targeted for deep imaging of the EoR. Finally, these selected fields are convolved with the synthesized beam of SKA1-low stations to ensure that the effect of sidelobes from the far-field bright sources is also weak.

Optimizing linear phased array transducers for non-destructive evaluation of thin layers

AbstractIn this work, a numerical method is proposed in order to achieve design optimisation of phased array (PA) probes for the special application of defects detection in thin films. This approach relies on an extended Fourier-based model that was adapted to predict the two-dimensional ultrasonic displacement field taking place in a thin plate under individual excitation of PA probe elements which have arbitrary orientation with respect to the examined part surface. Excitation is applied through a fluid couplant and is operated at scheduled delays that are managed to enable emission of constructive pulses. This gives the possibility to steer sound waves towards a direction and to focalize the beam in a selected point. An optimisation algorithm based on the concept of pattern search that does not require evaluation of a gradient was used to find the best match in the multidimensional analysis space of possibilities including the elements orientation angles, the elements lengths, the inter-elements distances and work frequency. Optimisation was performed with the objective to maximize the displacement amplitude at the focal point while minimizing simultaneously the effect of beam side lobes. The results obtained by this approach reveal that focalisation can be achieved with enhanced features in comparison with previous algorithms assuming linear elements that are parallel to the surface of the plate.

Image reconstruction for large FOV Airy beam light-sheet microscopy by a 3D deconvolution approach.

Airy beam light-sheet microscopy (LSM) has a very wide field-of-view and generates a high contrast image, which is a big advantage for large cubic sample imaging. Due to the effect of side lobes of Airy beam, shadow artifacts are incurred and therefore, proper image deconvolution is required to reconstruct the real image from the measured image. In this Letter, we propose a block-by-block reconstruction approach based on a 3D deconvolution algorithm, the Richardson-Lucy algorithm with roughness regularization, for Airy beam light-sheet microscopy (ALSM). The simulation and experimental results show that the proposed 3D deconvolution approach significantly outperforms the existing 1D deconvolution technique in restored image-quality, which makes it very promising for large field-of-view (FOV) ALSM image reconstruction.

Optimal linear filtering for weak target detection based on dyadic contrast function analysis in RFT

In this study, a forward model for radio frequency tomography (RFT) is improved to remove the effect of strong sidelobes from dominant scatterers in the region of interest. This approach uses a `suppression algorithm (SA)' to remove the effect of strong sidelobes on weak targets. SA is used to remove the effect of these strong sidelobes using the information from the dyadic contrast function (DCF). DCF is analysed in order to remove the effects of strong sidelobes generated by dominant cells in the measurement domain. The eigenvalues and eigenvectors for dominant cells are obtained to remodel the strong cells as a secondary source in the measurement scene. Furthermore, to simplify the inversion problem in the new forward model, iterative reconstruction algorithms is considered. Subsurface multiplicative algebraic reconstruction technique as additive technique is proposed to solve the new forward model RFT with less computing power and memory. The presented algorithm has been verified using simulated RFT data, generated by the computational electromagnetic software FEKO, for regular and irregular targets scenarios. The proposed research shows that using information from the DCF it is possible to obtain high quality imagery of buried weak targets in RFT.

The Closed-Form Expressions for the Bistatic Quantum Radar Cross Section of the Typical Simple Plates

Closed-form expressions for the bistatic quantum radar scattered by the circular and triangular plates with the single-photon incidence are derived in the field of the Fourier relationship between the surface atom distribution and the bistatic quantum radar cross section (BIQRCS). The proposed expressions are highly efficient useful tools to analytically estimate the BIQRCS of the typical simple plates in the condition of high frequency approximation. And the formulas have been preliminarily verified by the numerical solution for the typical incident angles. In addition, the analysis of the quantum effect of sidelobes of BIQRCS in scattering, which can be seen as a kind of quantum interference, is also presented. We expect that this achievement will apply to the modeling of bistatic quantum radar scattering.

New Side Lobe Cancellation Method of Linear Frequency Modulated Radar Signals

Pulse Compression (PC) technique has many advantages in signal processing of radar systems which enhances the radar performance. For a long pulse, the range detection capability can be increased with PC while maintain the advantage of resolution in range for uncompressed pulse. There are many PC techniques such as Binary and Linear Frequency Modulation (LFM) Codes, which can be utilize in radar. The radar detection performance is affected by unwanted signals, which called side lobes that may mask the weaker useful signals, which are present near to strong signals. Pulse compression that uses LFM code is discussed and contrasted with matched filter keep tracked of Hamming windowing filter technique to eliminate the level effect of side lobes. In the present paper, a proposed optimum filter is introduced to enhance both the radar detection capability and resolution in range. The proposed optimum filter representation is evaluated and compared with the classical matched filter response associated with Hamming windowing filter according to the representation of radar detection through Receiver Operating Characteristics (ROC) curves and resolution performance.

Fluorescence emission difference microscopy by superoscillation excitation.

A superresolution fluorescence emission difference (FED) microscopy based on superoscillation excitation is investigated. The solid superoscillation excitation spot is produced by the radially polarised Laguerre-Gaussian beam (LG), and the donut superoscillation excitation spot is produced by the same LG beam with spiral phase modulation. We show that the superoscillation excitation can enhance the spatial resolution of FED microscopy. When the ratio of the pupil radius and the second moment radius of the LG3,1 beam is 0.85 and the subtractive factor is 0.3, the resolution can be enhanced about 2 times than the general confocal microscopy. Compared with the general FED microscopy, the resolution can be enhanced about 1.1 times. Our simulations also demonstrate that two-view Richardson-Lucy (RL) deconvolution method can reduce the effect of side lobes, which is related to subtractive factor and pinhole. LAY DESCRIPTION: The fluorescence emission difference (FED) microscopy is a high-resolution light microscopy, which is based on the subtraction of images produced by two different confocal imaging modes. Here, the solid excitation spot is used in one imaging mode, and the donut excitation spot is in another imaging mode. There are various ways that the solid and donut excitation spots can be structured, but superoscillation excitation spots are still not used in the FED microscopy. Considering that the main lobe of superoscillation can be arbitrarily small in principle, we exploit the radially polarised Laguerre-Gaussian beam (LG) and spiral phase plate to produce superoscillation solid and donut spots. We present a detailed analysis about the performance of FED microscopy via superoscillation excitation. Our analysis is based on vector diffraction theory and supported by simulations of imaging. We find the proposed FED microscopy has better resolution than the confocal microscopy or the general FED microscopy excited by Gaussian beam. Especially, two-view Richardson-Lucy (RL) deconvolution method can reduce the negative impact of strong side lobes, which is related to the subtractive factor and the size of pinhole located at the detector.

The Simulation and Analysis of Quantum Radar Cross Section for Three-Dimensional Convex Targets

Quantum radar offers the prospect of detecting, identifying, and resolving RF stealth platforms and weapons systems, but the corresponding quantum radar cross section (QRCS) simulation is restricted—almost all existing methods can only be used for the two-dimensional (2-D) targets, not the 3-D targets even for convex targets. We propose a novel method that can deal with the calculation of the orthogonal projected area ( $A_{\perp}$ ) of the target in each incidence, which is the key part of QRCS simulation for the arbitrary 3-D convex target. To the best of our knowledge, this has not been reported before. In this paper, we introduce a three-step computation process of ( $A_{\perp}$ ), and verified the method for typical 2-D targets. Finally, we show some results for typical 3-D convex targets and compared the QRCS with classical radar cross section (CRCS). Meanwhile, we analyze the superposition of quantum effect of side lobes for 3-D convex targets. The proposed method provides a key improvement for realizing the universalization and utilization of QRCS calculation.

A Detection Method for Induction Motor Bar Fault Using Sidelobes Leakage Phenomenon of the Sliding Discrete Fourier Transform

The Fourier transform is widely used to diagnose induction motor faults through the monitoring of fault signatures from measured signals such as stator currents. For a good frequency resolution, Fourier transform needs a long signal acquisition time that increases the probability of speed fluctuations which, leads to fault signatures variations. In addition, limited acquisition time and acquired points generate unwanted sidelobes leakage phenomenon, caused by step frequency resolution. In signal processing, the use of window functions allows the avoidance of this phenomenon with the cost of losing a part of signal information. In this paper, the authors propose a new method for the diagnosis of induction motor broken bar fault based on sliding window discrete Fourier transform and the effect of sidelobes of sideband frequencies on the fundamental component amplitude of stator current. The main advantage of the proposed method is that one can detect the amplitude of the fault indicator frequency in vicinity of the fundamental one in shorter time and with good precision even if the motor turns at no-load when compared to used methods, as fast Fourier transform, zoom fast Fourier transform, multiple signal classification, and zoom multiple signal classification. The simulation and experimental results validate the effectiveness of the proposed method.

METHOD OF REMOVING AN EFFECT OF SIDE LOBES IN FORMING AN ULTRASOUND SYNTHETIC IMAGE

The present invention relates to a method of removing an effect of side lobes in an ultrasound synthetic image. The method includes: a) setting a plurality of scan lines and defining sequential indices upon the scan lines; b) setting a transmit order of a transmit beam for the scan lines in a non-sequential manner in which increment and decrement of the indices of the scan lines are repeated; c) transmitting the transmit beam based on the set transmit order to obtain a plurality of receive beams in response to each transmission of the transmit beam; d) grouping the receive beams to an increment group corresponding to an increment direction of the numbers of the scan lines and a decrement group corresponding to a decrement direction of the numbers of the scan lines; e) performing an auto correlation upon the receive beams included in the respective increment group and the decrement group; and f) applying weights to the auto correlation results and summing the weight-applied auto correlation results to thereby remove an effect of side lobes.

A NEW APPROACH FOR MOVING TARGET DETECTION USING BARTLETT METHOD FOR SPECTRAL ESTIMATION

Moving Target Detection (MTD) is an automated radar signal and data processing system, which is designed to improve the performance of radar systems in the presence of various forms of clutter. Consequently, it provides high probability of detection (Pd) for an acceptable probability of false alarm (Pia). It employs coherent, linear Doppler filtering, adaptive thresholding and a fine ground clutter map to reject ground clutter, rain clutter, birds, and interference. The current MTDs relay on the Fast Fourier Transform (FFT) of the total received data sequence to estimate the clutter power spectrum and consequently reduce or remove its effect on the detection performance. Direct FFT leads to high sidelobes level and requires a significant large computation time. The high level sidelobes increases the false alarm probability at the output of the Doppler filters bank. A solution for reducing the effect of spectral sidelobes is the utilization of window functions. However, this solution leads to widening the main spectral lobe and reduce the Doppler resolution. Also it increases the hardware complexity of the system. In the present work, Bartlett method for spectral estimation which depends on dividing the received data sequence into a number, K, of nonoverlapping segments and averaging the calculated FFT for each segment over K, is applied in the MTD instead of the direct FFT for typical ground based radar. The proposed method enhances the target detection capabilities, by providing higher detection probabilities, lower false alarm rates and an additional gain of 7-10 dB in the improvement factor, in the presence of ground and weather clutter, compared to the traditional one. This is because the sidelobe levels obtained are very small in magnitude. This in turns facilitates the realization of the Doppler filters bank without using additional weighting. The obtained performance can be achieved by applying the direct FFT with weighting function to the total received data sequence, which leads to a more hardware complexity and long time calculations compared to the proposed method. Computer simulation results are presented to support the superiority of the proposed technique.

Ultrasonic transmitting and receiving apparatus and ultrasonic transmitting and receiving method

An ultrasonic transmitting and receiving apparatus capable of obtaining high quality ultrasonic images with reduced effect of side lobes. The apparatus includes: an ultrasonic transducer array including ultrasonic transducers; a drive signal generating unit for generating drive signals for driving the ultrasonic transducers; a transmission control unit for controlling the drive signal generating unit such that ultrasonic waves transmitted from the ultrasonic transducers form at least one ultrasonic beam; a reception control unit for performing reception focusing processing on detection signals obtained based on the ultrasonic echoes to form a reception focal point thereby obtaining plural pieces of measurement data; a storage unit for storing plural different acoustic pressure intensity profiles; and an essential data calculating unit for calculating image data based on the plural pieces of measurement data and the plural different acoustic pressure intensity profiles.

The influence of window sidelobes on DFT-based multifrequency signal measurement

One of the causes influencing the uncertainty of the measured parameter is the mutual influence of the window spectra contained in the multifrequency signal spectrum. This paper analyses the effect of window spectrum sidelobes on the evaluation of multifrequency signal RMS value estimated by two DFT-based techniques (the “mainlobe method” and RMS value estimation using interpolated DFT). The RMS bias caused by window sidelobes when applying twelve different generalized cosine windows is compared. Both simulation results and theoretical relations are included. The presented principle is applicable for all DFT based algorithms, not only for those used for RMS value estimation.

Probing conformational changes of proteins by quantitative second-derivative infrared spectroscopy

Probing protein conformational changes plays a crucial role in protein structure and function studies. However, the lack of efficient biophysical techniques makes it difficult to obtain the distinct behaviors of different secondary structure elements in a protein upon perturbation. This paper presents a discussion of the two major problems, the effect of sidelobes and different half-width at half-height (HWHH) values, encountered in quantitative second-derivative infrared (QSD-IR) spectroscopy and introduces the development of two criteria for checking the validity of the results obtained using the QSD-IR method. It was found that neither the sidelobes nor the HWHH significantly affected the quantitative result of protein conformational changes by using poly- l-lysine and hemoglobin as model proteins. A case study of bovine serum albumin (BSA) thermal aggregation suggested that the thermal transition of BSA was a process involving sequential events, and the two helical components were found to have a distinct response to heat perturbation. These results were confirmed by two-dimensional infrared correlation spectroscopy and by results in literature, suggesting that the QSD-IR method might be a potentially powerful tool to probe the distinct response of different secondary structures to perturbation.

Effect of sidelobes on demultiplexing characteristics of a grating-folded directional coupler demultiplexer

The effect of sidelobes on the demultiplexing characteristics of a grating-folded directional coupler demultiplexer are investigated. The bit error-rate characteristics of the demultiplexed signal is examined, and a power penalty originated from the sidelobe is observed for the grating-folded directional coupler with conventional uniform grating. A phase-synchronized sampled grating is applied to suppress the sidelobe of a Bragg grating, and power-penalty-free demultiplexing is achieved in this structure.

Nonstationarity broadening reduction in pulsed Doppler spectrum measurements using time-frequency estimators.

The spectral width of Doppler signals is used as measure of lesion-induced flow disturbance. Its estimation accuracy is compromised using the conventional short-term Fourier transform (STFT) since this method implicitly assumes signal stationarity during the signal window while the Doppler signals from arteries are markedly nonstationary. The Wigner-Ville (WVD), Choi-Williams (CWD) and Bessel distributions (BD), specifically designed for nonstationary signals, have been optimized for spectral width estimation accuracy and compared to the STFT under different signal to noise ratios using simulated Doppler signals of known time-frequency characteristics. The optimum parameter values for each method were determined as a Hanning window duration of 10 ms for the STFT, 40 ms for the WVD and CWD and 20 ms for the BD and dimensionless time-frequency smoothing constant values of five in the CWD and two in the BD. Thresholding was used to reduce the effect of cross terms and side lobes in the WVD and BD. With no added noise the WVD gave the lowest estimation error followed by the CWD. At signal-to-noise ratios (SNR's) of 10 dB and 20 dB the CWD and BD had similar errors and were markedly better than the other estimators. Overall the CWD gave the best performance.